FR2566918A1 - System for obtaining summarised information on the line spectrum provided by the spectrum analyser of a Doppler radar - Google Patents

Abstract

The system comprises a demultiplexer 21, a series-parallel transformer 22 and two encoders 25, 26 for determining a target detection signal D and the position G, F of the first and last logical levels I of the elementary raw plot PBE. An adding circuit 29, two comparators 27, 30, a counter 23 and an AND gate 31 make it possible to produce a signal indicating whether the target has a uniform speed V. An arithmetic and logic unit 28 and an exclusive OR gate 32 determine the spectral estimate ES of the target, and a counter 24 gives the spectral bandwidth SP of the radar cells. Application to Doppler radars.

Description

 The present invention relates to a system making it possible to obtain summary information of the line spectrum provided by a spectrum analyzer of a Doppler radar.

In this radar, the speed of the target is obtained from the frequency offset due to the movement of this target. In the context of a radar with diversity of emission frequencies, a different Doppler frequency offset corresponds to each transmitted frequency. If Fe. Is the emission frequency of index i (with i = I to N) and if each emission frequency is associated with a different recurrence frequency, or sampling frequency Fs., It will therefore be to obtain a measurement of the Doppler frequency shifts associated with each pair (fi., Fsi).
ii comparison of the N values, each associated with a couple (fez, Fsi), which makes it possible to decide what is the true value of the frequency offset associated with this couple and which therefore makes it possible to remove the ambiguity in speed.

 The system uses words of 2m binary elements, m being a natural integer, called elementary raw plots, supplied by a contrast detector placed at the output of a spectrum analyzer, and supplies, from this information received, summary information. A monocinetic target is, in fact, detected for several contiguous lines of the spectrum analyzer. The measurement will therefore not consist of a single value of the frequency but of a set of n contiguous values.

We show (property of the Fourier transform at sixteen points after Tchebycheff weighting with sixty decibels of rejection) that a
2m monocinetic target is detected for at most 2m + 1) cyclically contiguous lines of the spectrum analyzer, i.e. it provides at most
2m 2m (4 + 1) lines of sufficient level for at most 2m + 1) values of (4 known Doppler frequency shifts. In order to reduce the computation volume necessary for determining the target's speed, we wish to reduce d '' one way or another these contiguous lines in a single value which summarizes them.This is the goal of the system, called plot summarizer which, moreover, must differentiate the monocinetic targets from those which are not, so avoid giving summary values that have no direct physical meaning.

Thus, the object of the invention is to define a plot summary providing, for each distance corresponding to a given delay of the received signal, a digital signal called summary summary plot, consisting of a binary element of target presence, dlun binary element indicating if this target is monocinetic and of a word of (m + l) binary elements containing, possibly, information on the speed of this target, called spectral estimate, likewise providing a digital signal of (m + l) binary elements containing information on the spectral congestion of the radar cells, and receiving a contrast detector, and for each of these distances, two digital signals called elementary raw plots consisting of a word of 2m binary elements, this contrast detector receiving itself a signal provided by a 2m point spectrum analyzer consisting of a weighter, a 2m point Fourier transformer and a module extractor, the weighting performed by the weighter being such
m that it limits to (24 + 1) the number of cyclically contiguous lines for which a monocinetic target is detected.

 One solution consists in addressing read only memories, containing the elementary summary plots, by the elementary crude plots as in the method described in the French patent application No. 81 20644 (2 515 829) filed on November 4, 1981 by the applicant and entitled " System allowing to obtain a summary information of the line spectrum provided by the spectrum analyzer of a Doppler radar ".

In the context of the present invention, it is planned to delete these read-only memories and to use means constituted by logic circuits comprising: - first means for obtaining a digital signal giving
the spectral congestion of each radar cell from the gross plot
elementary with fixed thresholds; and - second means for obtaining the compound elementary summary plot
of a target presence binary element, of a binary element
indicating whether the target is monocinetic and information on the
target speed.

The invention will be better understood and other characteristics and advantages will appear with the aid of the description below and of the attached drawings in which - FIG. I represents a block diagram consisting of the analyzer of
spectrum, contrast detector and plot summary according to
the invention; - Figure 2 shows in a) a signal supplied by a
spectrum with sixteen lines, in b) the signal supplied by the detector
contrast, in c) a possible value of the spectral estimate and in d)
the elementary raw block; and - Figure 3 shows an embodiment using the solution according to the invention.

FIG. 1 represents a block diagram comprising a spectrum analyzer 1 and a contrast detector 2 supplying two words of sixteen binary elements PBEV, PBEF to the plot summarizer 3. The spectrum analyzer 1 receives, from the radar receiver, a video signal on its input E. it consists of a weighter 11, a transformer of
Fourier 12 at sixteen points and a module extractor 13. This spectrum analyzer provides sixteen digital information on the amplitude of the lines of the spectrum of the analyzed signal represented in a of figure 2.

A contrast detector 2, with sixteen thresholds SO to S15, receives this sixteen digital information and supplies a word of sixteen binary elements represented in d) of FIG. 2, calculated from sixteen fixed thresholds and corresponding to the presence or to the absence of lines higher than the corresponding thresholds in the useful spectrum of the analyzed signal, this word being called elementary raw plot with fixed thresholds PEEF, and a word of sixteen binary elements, calculated from sixteen thresholds determined by means of the average of lines of same order of one or more spectra preceding or following the spectrum considered, this word being called elementary rough plot with variable thresholds PBEV. When the variable thresholds are not calculated, the elementary raw plot with variable thresholds PBEV has all its binary elements at logic level I. The plot summary 3 is responsible for determining a word of five binary elements, called spectral congestion SP of each cell radar, which represents the number of overruns of the fixed thresholds, and to concentrate the information contained in the elementary gross plot with fixed thresholds FEEF, or in the elementary gross plot with variable thresholds PBEV, if these are calculated, so as to make it more easily usable in possible calculations. The output of the plot summarizer 3 therefore gives an elementary summary plot PRE, in the form of a word of seven binary elements, composed - of a first binary element D, of presence of target, which is at
logic level 1 if at least one binary element of the elementary raw plot
be considered PEEF, PBEV is at logical level 1, in which case there is
presence of target; - a second binary element V, indicating whether the target is monocine
tick, which is at logic level I if the elementary gross stud consi
PBEV, PBEF has a single group of at least one and
plus five binary elements cyclically joined at logical level 1,
shown in b) of Figure 2, the other bits being
at the logical level O (property of the Fourier transform after
weighting of Tchebycheff with sixty decibels of rejection),
in which case the target is monocinetic; and - a word of five binary elements, called spectral estimate ES represented
felt in c) of figure 2, giving, if there is presence of mono target
kinetics, the position of the middle of the grouping of binary elements
cyclically contiguous in the elementary gross stud PBEV, PBEF
considered.

It should be noted that the spectral estimate has five binary elements, because there are thirty-two possible positions of the medium in an elementary raw plot of sixteen binary elements. A COM command makes it possible to select either the raw elementary plot with fixed thresholds PBEF, or the elementary rough plot with variable thresholds PBEV, if these are calculated, for the determination of the elementary summary plot PRE.

 FIG. 3 represents a more detailed functional diagram of the pad summarizer according to the invention. In this FIG. 3, a multiplexer 21, with inverters at the input, selects, as a function of the value of a COM command, the complement of the basic raw block PBEF with fixed thresholds or of the basic raw block PBEV with variable thresholds, if these are calculated. The output of said multiplexer 21 is connected to the input of a counter 23 and a series-parallel transformer 22. The counter 23 gives the number of logic levels 1 of the complement of the elementary raw pad considered on a word of four binary elements The series-parallel transformer 22 delivers as output the complement of the elementary raw pad considered, in the form of a word of sixteen binary elements in parallel PBE, and an inversion signal P at logic level O if the two elements extreme binaries of said word are at logical level O and at logical level I in other cases.

A first encoder 25, placed at the output of the parallel parallel transformer 22, gives the position G of the first logic level O from the start of the word of sixteen binary elements PBE if the inversion signal P is at logic level 1, or the same position G in the word of sixteen binary elements PBE whose extreme bytes are inverted if the inversion signal P is at logic level 0. A second encoder 26, placed at the output of the series-parallel transformer 22, gives the position F of the first logical level O from the end of the word of sixteen binary elements PBE if the inversion signal P is at logic level 1, or the same position F in the word of sixteen binary elements PBE whose extreme bytes are inverted if the inversion signal P is at logic level 0, as well as information at logic level I when there is presence of at least one logic level O in the word PBE. This information gives the binary element D of target presence. Said positions E and G, delivered in the form of words of four binary elements in parallel, are sent to an adder 29, with two inputs of four binary elements, responsible for summing them. The output of this adder is sent to a first comparator 30 , with two inputs of four binary elements, which compares it to the output of the first counter 23, and whose output is at logic level I when there is equality, that is to say when there is a block unique of cyclically contiguous logical levels O in the elementary raw plot considered. A second comparator 27, connected to the output of the counter 23, has its other input of four binary elements at the value 11, and determines whether the number of logic levels i of the complement of the elementary raw plot considered is greater than or equal to 11. Thus , the output of said comparator 27 will be at logic level I if the number of logic levels O is less than 6 in the elementary raw block considered. Said output is connected, with the output D of presence of target of the second encoder 26 and the output of the first comparator 30, to an AND gate 31 with three inputs whose output is therefore at logic level 1 when the complement of the elementary raw pad considered has a single block of cyclically contiguous logic levels 0 whose number is less than or equal to 5, this giving the binary element V indicating whether the target is monocinetic. This binary element is sent to an arithmetic and logic unit 28, which has its inputs connected to the outputs of the first and second encoders 25 and 26. Said arithmetic and logic unit 28 subtracts, at the output of the first encoder 25, the output of the second encoder 26 and a constant equal to 1. The inverse of the carry C of the arithmetic and logic unit 28 is sent to an exclusive OR gate 32 with two inputs with the inversion signal P. This exclusive OR gate 32 gives the Most significant bit of information about the target speed or ES spectral estimate. The four least significant binary elements of the spectral estimate ES are given by the output of the arithmetic and logic unit 28. If the inversion signal P is at logic level O and if the inverse of the carry C is at logic level 1, that is to say when the result of the arithmetic and logic unit 28 is negative, the output of gate 32 is at logic level 1; on the other hand, if the inverse of the carry C is at logic level 0, that is to say when the result of the arithmetic and logic unit 28 is positive, the output of gate 32 is at logic level 0. If the inversion signal P is at logic level 1 and if the inverse of the carry C is at logic level 1, the output of gate 32 is at logic level O; on the other hand, if the inverse of the carry C is at the logic level o, the output of the gate 32 is at the logic level 1. Thus, we add to the result of the arithmetic and logic unit 28 a constant equal to 16 If the inversion signal P is at logic level i, that is to say if the complement of the elementary raw block PHEF, PBEV considered does not have its two extreme bytes inverted; on the other hand, a constant equal to 32 is added if the inversion signal P is at logic level 0, that is to say if the complement of the elementary raw block PEEF, PBEV considered has its two extreme bytes inverted, and this , modulo 32.The outputs of gate 32 and of the arithmetic and logic unit 28 give, in the form of a word of five binary elements, the spectral estimate ES of the elementary summary plot PRE, unless the output of the gate AND 31 is at logical level 0, in which case the output of the arithmetic and logical unit 28 is at logical level 0, the spectral estimate ES having no physical meaning. A counter 24, receiving the elementary raw block with fixed thresholds PBEF gives the spectral congestion SP of each radar cell in the form of a word of five binary elements representing the number of logic levels 1 in said raw raw block with thresholds PBEF fixed.

Of course, the embodiment described is in no way limitative of the invention; in particular, the invention could have been described from a spectrum analyzer with thirty-two lines or, more generally, with 2m lines. The target speed information must then be given by a word of (m + 1) binary elements and the maximum number of lines, for which a monocinetic target is detected,
2m is then (4 + 1) for a weighting of Tchebychef f at sixty decibels of ejection.

Claims (6)

 1. Pad summarizing device receiving, for each distance, corresponding to a given delay of the received signal, two digital signals called raw elementary pads (PBEF; PBEV), consisting of a word of 2m binary elements, m being a natural integer, and supplied by a contrast detector comparing the lines, coming from a 2m point spectrum analyzer, to either fixed thresholds, or thresholds calculated from lines of the same order from one or more preceding and following spectra, the number cyclically contiguous lines for which a limited kinetic target is detected  2m to (4 + 1) maximum and said device providing, for each of these distances, a digital signal called elementary summary plot (PRE) consisting of a binary element of presence of target (D), of a binary element ( V) indicating whether this target is monocinetic and of a word of (m + l) binary elements called spectral estimate (ES) containing information on the speed of the target, characterized in that said device comprises - first means (24 ) to obtain a digital signal from  (m + l) binary elements giving the number of lines of the spectrum  exceeding the fixed thresholds starting from the elementary gross stud with thresholds  fixed (PBEF) and representing the spectral congestion (SP) of each  radar cell; and - second means (21 to 23, 25 to 32) for obtaining the elements  binaries indicating the presence of target (D), indicating whether the target  is monocinetic (V) and gives information on the speed of the  target, composing the elementary summary plot (PRE), from one  elementary raw pads (PBEV, PBEF), said means being constituted by logic circuits.  2. pad summarizing device according to claim 1, characterized in that said second means comprise - third means (21, 22, 26) providing the binary element of  presence of target (D) at logic level I when at least one of  binary elements of the elementary raw plots (PBEF, PBEV) is at  logic level 1; - fourth means (21 d 23, 25 to 27, 29 to 31) providing  the binary element (V), indicating that the target is monocinetic, at  2m  logic level I when at most (4 + 1) bits  cyclically contiguous of the elementary rough blocks (PBEF, PBEV) are  at logical level 1 ;; and - fifth means (28, 32) providing a word of (m + 1) elements  binaries giving information about the speed of the target, called  spectral estimate (ES), indicating the position of the middle of the group of  cyclically contiguous logic levels 1 of the elementary raw plot  considered (PBEF, PBEV).  3. pad summarizing device according to one of claims 1 or 2, characterized in that said third means are constituted by a multiplexer (21) selecting, depending on the value of a command (COM), one of two elementary raw pads (PBEF, PBEV), the output of which is connected to the input of a series-parallel transformer (22), giving an inversion signal (P) on a binary element and the elementary raw pad considered (PBE) on a word of 2m binary elements, by an encoder (26), connected to the two outputs (P, PBE) of the parallel-serial transformer (22), giving, according to the value of the inversion signal (P), the position (F) of the first logical level 1, from the end of the word, of the elementary raw plot (PBE), the two extreme blocks of 2 binary elements of which have been interchanged or not, on a word of m binary elements, and an item of information presence of logic levels i, giving the binary element (D) of target presence.  4. A pad resuming device according to any one of claims 1 to 3, characterized in that said fourth means consist of another encoder (25), connected to the two outputs (P, PBE) of the series-parallel transformer (22) , giving, according to the value of the inversion signal (P), the position (G) of the first logic level 1, from the start of the word, of the elementary raw pad (PBE), of which the two blocks  mI extremes of 2m 1 binary elements have been interchanged or not, on a word due m binary elements, by a counter (23), connected to the output of the multiplexer (21), giving the number of logic levels O on a word of m binary elements, by a first comparator (27) comparing the output  3m from said counter (23) to a constant 34 2m-1, by an adder (29), connected to the output of said encoders (25, 26) and giving the sum of the two positions (G, F) on a word of m elements binary, connected to a second comparator (30), the other input of which is connected to the output of the counter (23) and the output of which is connected to one of the three inputs of an AND gate (31), connected to even at the target presence output (D) from the encoder (26) of the third means and at the output of the first comparator (27), and delivering the binary element (V), indicating that the target is monocinetic, when there is a single block of cyclically contiguous logic levels i in the elementary raw plot considered (PBEF, PBEV).  5. A pad summarizing device according to any one of claims 1 to 4, characterized in that said fifth means consist of an arithmetic and logic unit (28)> connected to the output (V) of said AND gate (31) and at the outputs with m binary elements of said coders (25, 26) and whose outputs give the result obtained by subtracting the output of the coder (26) from the third means plus a constant equal to 1 from the output of the coder (25) from the fourth means , on a word of m binary elements, and by an exclusive OR gate (32) with two inputs receiving the inversion signal (P) and the inverse of the carry (C) of the arithmetic and logic unit (28) , and allowing to obtain at output the most significant binary element of the information on the speed of the target by adding, to the result of the arithmetic and logical unit (28), the constant 2m, or 2m + 1, according to the value of the inversion signal (P) and this, modulo 2m + 1, said binary element and the outputs of the arithmetic unit ic and logic (28) giving the spectral estimate (ES).  6. pad summarizing device according to any one of claims 1 to 5, characterized in that said first means consist of a counter (24) outputting a word of (m + 1) binary elements indicating the number of levels Logic I of the elementary raw plot (PBEF) with fixed thresholds.